As the performance of an information processing device such as a server, or the large scale integrated circuit (LSI) device has been improved, the data rate of data signals transmitted and received between the devices or within the device has increased. However, the improvement of an operation speed of a circuit or a device within the device becomes strict recently, so that a multi-level transmission technology, such as the pulse amplitude modulation 4 (PAM4), is proposed to be adopted as a technology for improving the data rate without increasing an operation speed. When the same amount of information as the non return to zero (NR) is transmitted in the PAM4, the change speed (baud rate) of data signals may become halved.
However, in a reception circuit used in an information processing device or an LSI device, the CDR that reproduces a value (data) and a clock signal from a transmitted data signal is performed. In the CDR, in order to determine the value with appropriate timing, a phase detecting circuit for detecting the phase difference between a sampling clock signal for sampling a data signal and a data signal is used.
The phase detecting circuit includes a phase detecting circuit in the mueller-muller (MM) type which detects the phase difference by 1× sampling, and a phase detecting circuit in the bang-bang (BB) type which detects the phase difference by 2× sampling. Further, the 1× sampling indicates one time sampling for one symbol (which is also called one unit interval (UI)) of a data signal. The 2× sampling indicates two time sampling for one symbol of a data signal. The data signal of the NRZ has a value of 1 bit per symbol, and the data signal of the PAM4 has a value of 2 bits per symbol.
Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 03-016337.
Related technologies are disclosed in, for example, K. H. Mueller to and M. Muller, “Timing Recovery in Digital Synchronous Data Receivers,” IEEE Transactions on Communications, vol. COM-24 pp, 516-531, May 1976.